SUMMARY OF WORK. [unreadable] [unreadable] A randomized clinical trial of the effects of device-guided slow breathing exercises on 24-hr ambulatory blood pressure in persons with prehypertension and mild hypertension was completed during the past year. The study produced two sets of findings, one concerned with the acute effects of device-guided breathing on respiratory behavior, and another with the effects of four weeks of daily practice of device-guided breathing on resting and 24-hr blood pressure. A control group of patients who simply focused attention on breathing during daily 15 min sessions for four weeks was also studied. Below are abridged abstracts from two manuscripts that describe the main findings.[unreadable] [unreadable] Acute Respiratory Effects of Guided Slow Breathing in Prehypertension and Hypertension:[unreadable] Background. The present study hypothesized that increases in tidal volume that accompany guided breathing (GB) result in progressive decreases in pCO2, as indicated by decreases in end tidal CO2 (PetCO2) . [unreadable] Methods. Persons with prehypertension or mild hypertension were trained to perform a 15-min DGB task. Respiration, blood pressure, heart rate, and PetCO2 were recorded during a 10-min pre-task interval, the 15-min guided breathing task, and a 10-min recovery interval.[unreadable] Results. GB was accompanied by progressive decreases in PetCO2 and decreases in systolic blood pressure. Following task cessation, PetCO2 remained below pre-task levels for more than 10 min. 24-hr urinary output of marinobufagenin, a compound that co-varies with plasma volume, was greater in participants with higher 24-hr blood pressure levels in this group of patients.[unreadable] Conclusion. The antihypertensive effects of DGB could include the effects of decreased pCO2 on renal regulation of sodium with consequent changes in plasma volume. [unreadable] [unreadable] Blood Pressure and Respiratory Effects of Daily Practice of Device-guided Breathing:[unreadable] Background. The present study in patients with prehypertension or mild hypertension investigated the extent to which changes in breathing pattern at rest accompany the antihypertensive response to repeated daily practice of GB.[unreadable] Methods. Twenty pre-hypertensive or mildly hypertensive individuals were trained to slow breathing <10 breaths/min during 15 min sessions via auditory pacing, and practiced the exercise daily at home for four weeks. A control group (FB) of equal size was instructed to focus attention on breathing for 15 min daily for four weeks. Breathing pattern, end tidal CO2 (PetCO2), and blood pressure were monitored before and after the intervention. [unreadable] Results. Resting systolic and diastolic BP were decreased following four weeks of daily GB. Smaller decreases in systolic and diastolic BP were observed after four weeks of daily FB. Participants who showed the largest decreases in clinic blood pressure also showed the largest increases in resting tidal volume. Neither GB nor FB decreased 24-hr blood pressure or overnight breathing pattern.[unreadable] Conclusions. These results confirm that daily practice of DGB can decrease resting blood pressure, and show that such effects are associated with specific changes in breathing pattern at rest. Whether daily practice of GB did not decrease 24-hr blood pressure due to initial blood pressure levels, duration of practice, or other factors remains to be determined.[unreadable] [unreadable] In addition, a study of breathing variability in persons at rest as a function of their 24-hour blood pressure was completed. An abstract of the results of this study is provided below.[unreadable] [unreadable] Breathing Variability at Rest is Positively Associated with 24-hr Blood Pressure Level[unreadable] Background. The present study hypothesized that the variability of breathing and end tidal CO2 (PetCO2) in seated women at rest is positively associated with their 24-hr blood pressure level.[unreadable] Methods. Breath-to-breath measures of breathing rate and tidal volume were recorded via inductive plethysmography in each of 54 women during two 20 min sessions of seated rest, and in 32 women during nighttime sleep. PetCO2 was also recorded during these sessions via a respiratory gas monitor. Ambulatory blood pressure was recorded for 24 hr between the two clinic sessions via oscillometry. [unreadable] Results. Breath pauses > 10 sec were observed significantly more often in women in the upper than the lower tertile of 24-hr systolic blood pressure. Breath-to-breath variability in breathing rate, tidal volume, and minute ventilation were greater in the higher blood pressure tertile women. Variability in PetCO2 was also greater in high blood pressure tertile women. These associations were independent of age, weight, and body surface area. Breathing variability was inversely correlated with heart rate variability.[unreadable] Conclusion. Greater variability in breathing at rest that is independent of metabolic activity characterizes women with prehypertensive blood pressure. The linear association of breathing variability with 24-hr blood pressure level is consistent with the hypothesis that intermittent breathing inhibition may predispose to the development of some forms of hypertension.[unreadable] [unreadable] Together, these studies support the view that breathing pattern can play a significant role in blood pressure regulation, especially salt-sensitive forms of hypertension. Future research is designed to apply an ambulatory recording of end tidal CO2 in the natural environment to control of blood pressure in hypertensive patients. The monitor has been miniaturized, is battery powered, and is capable of providing immediate auditory feedback for variations in breathing pattern. Studies will focus on its validation and reliability in ambulatory humans, with the identification of disordered breathing in hypertensive patients, and with the development of a behavioral intervention that combines training in adaptive breathing habits with dietary sodium regulation designed to decrease 24-hr blood pressure in hypertensive patients. Successful implementation of this new technology could lead to prevention and reversal of the most common of cardiovascular disorders.